THIS INVENTION relates to an external rotor brushless DC motor.
For many years external rotor brushless DC motors have been manufactured in accordance with a conventional topography. An example of such a conventional topography of a brushless DC motor is shown in FIG. 1 of the accompanying drawings. The basic premise of this topography is that the stator assembly has a stator assembly base with a recess therein. The driving and control circuitry for the motor is attached to the stator assembly base in the recess, the stator windings being located above the circuitry such that the circuitry is sandwiched in the recess between the stator windings and the stator assembly base. Typically, the stator windings and the circuitry are permanently affixed to the stator assembly base.
Despite drawbacks associated with this topography, there have been little or no attempts to deviate from the conventional topography described above since this type of motor was first made over 20 years ago.
There are a number of drawbacks associated with the above described conventional motor topography. These drawbacks all stem from the conventional location of the printed circuit board at a position between the stator assembly base and the stator windings. For example, since the stator windings are almost always permanently affixed to the stator assembly base, it is extremely difficult to modify or repair the circuitry or components on the printed circuit board without at least partially damaging or destroying the stator windings, or the assembly base. It is often the case that it is cheaper to scrap a motor rather than to attempt to repair or maintain the circuitry associated with the motor.
A further drawback is that it is difficult to dissipate heat, generated by both the motor and the circuitry on the printed circuit board, away from the motor.
Another drawback is that it is difficult to seal the printed circuit board and the components thereon from the ingress of dust and moisture.
A further drawback is that it is also difficult to dissipate the heat, generated by both the motor and the drive circuitry on the printed circuit board, which in many cases restricts the power output of the motor.
It is an object of the present invention to seek to provide an external rotor brushless DC motor which does not suffer from the above-mentioned drawbacks.
Accordingly, one aspect of the present invention provides an external rotor brushless DC motor comprising: a stator assembly base having a base plate; a winding assembly affixed to the stator assembly base; and circuitry associated with the motor, wherein the base plate is disposed between the circuitry and the winding assembly and is provided with a cover to define an enclosure, the circuitry being located between the base plate and the cover within the enclosure which is hermetically sealed.
Preferably, the circuitry is attached to or supported by the base plate.
Conveniently, the base plate comprises a substantially circular base plate having a substantially cylindrical side wall, the side wall defining a recess within which the circuitry is located.
Advantageously, the stator assembly base include means for supporting the stator windings.
Preferably, the stator assembly base is manufactured from aluminium or any other material with good thermal conduction.
Conveniently, the circuitry is in the form of a printed circuit board having a plurality of components mounted thereon, the components on the printed circuit board being positioned on either or both surfaces of the printed circuit board.
Preferably at least some, if not all of the high power dissipating components on the printed circuit board can overhang the printed circuit board and be attached to the assembly base P, hence conducting the heat directly into the assembly base, alternatively the heat dissipating components can be located over an aperture in the printed circuit board allowing them to be clamped to a projecting area on the assembly base so conducting the heat into the assembly base.
Another aspect of the present invention provides a fan incorporating a motor embodying the present invention.
Advantageously, the fan has a frame which is manufactured from a plastic material or other low cost easily manufactured material.
Conveniently, the motor has a cover plate and the cover plate comprises a part of the fan housing which is so constructed that the outer edge of the assembly base is in the airflow of the fan and hence cooled by the said airflow.
In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: